Enterprise conferencing with dual mixing

ABSTRACT

A method and computer readable medium for providing Enterprise conferencing is provided. In an exemplary embodiment of the invention, a first SIP INVITE message is exchanged between a Media Gateway of the Enterprise and a first Media Server of a Conferencing Service Provider. Then, an Application Server of the Conferencing Service Provider establishes conference call resources at the Conferencing Service Provider. A first RTP session is established between the Media Gateway and the first Media Server, and then a PROMPT AND COLLECT message is sent from the Application Server to the first Media Server to gather data from the caller for establishing the Enterprise conferencing. After receipt of the data by the Application Server, an SIP INFO message is sent from the Application Server to a second Media Server of the Conferencing Service Provider, selecting the second Media Server to host the call.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority to U.S.patent application Ser. No. 14/150,204, filed Jan. 8, 2014 and titledEnterprise Conferencing With Dual Mixing, which is a continuation of andclaims priority to U.S. patent application Ser. No. 12/139,540, filedJun. 16, 2008 and titled Enterprise Conferencing With Dual Mixing, nowissued U.S. Pat. No. 8,638,696 which is a continuation-in-part of andclaims priority to U.S. patent application Ser. No. 12/039,380, filedFeb. 28, 2008 and titled Enterprise Conferencing with Dual Mixing, nowissued U.S. Pat. No. 8,458,253, all of which are hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention is a system, method, and computer readable mediumfor providing audio/video/data conferencing to an enterprise that hasboth internal and external entities joining a conference.

Currently, many service providers offer conferencing services toenterprises that support callers both internal and external to theenterprise. Typically, these services are provided by conferencingservers located at centralized data centers which are often co-residentwith Public Switched Telephone Network (PSTN) ingress/egress points.

When a conference is setup, individual calls from the enterprise arebackhauled to the data center through either a public or private, voiceor data network. The problem with this approach is that backhauling allof the individual call legs takes a significant amount of bandwidth, andthus adds cost to the service provider which is often, in turn, passedonto the enterprise customer.

Therefore, what is needed to overcome the aforementioned limitation, isa system in which the enterprise legs of a conference can be combinedbefore being backhauled to the conference service and a method formanaging a conference in such a system. What is also required is theability to maintain enterprise originated conference calls at theenterprise premise and bridge external participants as needed to theenterprise from other conference service providers.

BRIEF SUMMARY OF THE INVENTION

The present invention, in exemplary embodiments, overcomes the abovedisadvantages and other disadvantages not described above. Also, thepresent invention is not required to overcome the disadvantagesdescribed above, and an exemplary embodiment of the present inventionmay not overcome any of the problems described above.

The present invention, accordingly, eliminates the need for each leg ofa conference to require its own, individual backhaul entity to theconferencing data center. This is accomplished by establishing equipmentat the enterprise entity that allows each conferencing leg exiting thePublic Branch Exchange (PBX) or similar entity at the enterprise to bemixed and converted to a consolidated, Internet Protocol (IP) stream forprocessing over an IP Network. Certain entities of the ConferencingService Provider's network are repeated at the enterprise premise toperform this consolidation. A Media Gateway is used at the enterprisesite to:

-   -   mix all conferencing legs leaving the enterprise;    -   convert PBX multi-media conference signaling formats to a        consolidated IP stream for communication with the Conferencing        Service Provider;    -   serve as proxy server for interfacing with Conferencing Service        Provider Application Server and local Media Servers.

Media Servers would reside at the enterprise premise for the hosting ofenterprise conferences locally to the enterprise location. These unitswould also serve as Voice over IP (VoIP) interfaces with the MediaServers located at the Conferencing Service Provider's site asconference participants external to the enterprise join the conference.

By having a Media Gateway and Media Servers at the enterprise premise,it allows conferences established from the enterprise to be served atthe enterprise with no backhaul connectivity required to theConferencing Service Provider. As external conference participants jointhe conference, a single IP connection over the Wide Area Network (WAN)and interfaced with the Conferencing Service Provider for both signalingand bearer traffic would be used to join these external conferenceparticipants to the local enterprise conference. As additionalconference calls are required to be established and served from theenterprise, the same IP connection can be used, therefore eliminatingthe need for multiple connections to be established back to theConferencing Data Center for processing and thus eliminating theadditional cost associated with providing and maintaining theseconnections.

Thus, in one aspect, the present invention is directed to a method forproviding Enterprise conferencing. A first SIP INVITE message isexchanged between a Media Gateway of the Enterprise and a first MediaServer of an Enterprise. Then, an Application Server of the ConferencingService Provider establishes conference call resources at theConferencing Service Provider. A first RTP session is establishedbetween the Media Gateway and the first Media Server, and then a PROMPTAND COLLECT message is sent from the Application Server to the firstMedia Server to gather data from the caller for establishing theEnterprise conferencing. After receipt of the data by the ApplicationServer, a SIP INFO message is sent from the Application Server to asecond Media Server of the Enterprise, and the second Media Server isselected to host the call.

In another aspect of the invention there is a method for joining aconference call hosted at an Enterprise, comprising: entering addressdata by a caller into a communication device to initiate a call to joinan established conference call, the address information indicating alocation of the conference call; connecting the communication devicewith a Media Gateway at the Enterprise through a PSTN; sending a SIPINVITE message from the Media Gateway to a first Media Server at aConferencing Service Provider; sending a CALL WAITING message from thefirst Media Server to an Application Server; verifying at theApplication Server that the caller has access privileges for theestablished conference call, and upon verification, sending an ACCEPTCALL message from the Application Server to the first Media Server;sending a SIP OK message from the first Media Server to the MediaGateway in response to the ACCEPT CALL message; and acknowledging theSIP OK message by sending a SIP ACK message from the Media Gateway tothe first Media Server.

Any of the exemplary methods of the invention may implemented bycomputer readable medium which includes instructions for executing themethods.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 depicts a typical configuration of how users on an EnterpriseSystem currently interface back to a Conferencing Service Provider viathe PSTN Network for establishing or joining a pre-existing conferencecall in accordance with a preferred embodiment of the present invention;

FIG. 2 depicts the addition of Conferencing Media Gateway and MediaServers at the Enterprise site and the required physical connectivity tothe WAN in accordance with a preferred embodiment of the presentinvention;

FIG. 3 depicts a further refinement of FIG. 2 by showing the logicalconnectivity of the embodiment and software protocols used to establishand maintain conference calls in accordance with a preferred embodimentof the present invention;

FIG. 4 depicts actual Session Initiated Protocol (SIP)/Real TimeReservation Protocol (RTP) message flows required for the Enterprisecaller to establish or join a conference call in accordance with apreferred embodiment of the present invention.

FIG. 5 depicts actual Session Initiated Protocol (SIP)/Real TimeReservation Protocol (RTP) message flows required for the external PSTNcaller to join a conference call at the enterprise premise in accordancewith a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the principles of the invention, Enterprise Systemslooking to reduce the cost of maintaining expensive PSTN connectivityfor conference call activity establish premise equipment (Media Gatewayand Media Servers) to allow connectivity directly to the ConferencingService Provider via the Wide Area Network (WAN). This allows theEnterprise System to bypass PSTN connectivity for all conference callactivity and ultimately reduce the cost of maintaining multiple PSTNconnections for this use.

With reference now to the figures and in particular with reference toFIG. 1, a diagram of a Enterprise Telephony System interfaced to aConferencing Service Provider is depicted in accordance with a preferredembodiment of the present invention. It should be noted that each devicerepresented can have multiple instances within the architecture. FIG. 1depicts only one instance of each entity for simplification purposes.Enterprise 185 represents any size business or organization requiringconferencing services from an external conferencing service provider.Enterprise 185 is represented herein as containing multiple Callers 100connected to a Public Branch Exchange 105 or similar entity known in theart for serving business telecommunication needs. Callers 100 can be anymultitude of entities within the Enterprise 185 and is beyond the scopeof this invention. FIG. 1 represents multiple Caller 100 entities toclearly depict the problem of PSTN connectivity required as multiplecallers exist in an Enterprise. “Caller”, as referenced in thisembodiment, will represent either a conference host or conferenceparticipant. Conference host is defined as a user who is establishingand hosting a conference call. Conference participant is one of possiblemany participants that will join a conference that another “Caller” ishosting. “Callers” can reside at the enterprise or at the PSTN and canbe either conference hosts or conference participants. Connectivitybetween the Caller 100 and PBX 105 can be in any format or mediumsupported by the PBX. For clarity purposes, this invention assumes thatthis connectivity is a typical Time Division Multiplexed (TDM)circuit-switched connection. The PBX serves as the switching entity andtelecommunications application server within the Enterprise 185. Itroutes calls as required between internal callers within the enterpriseand also routes internal callers to external interfaces outside of theEnterprise 185 via the PSTN 175.

The PBX 105 interfaces with the PSTN 175 via multiple Circuit-SwitchedConnections 110. These connections are typical DS1/E1 interfaces thatare well known in the art. These connections are usually leased from thePSTN service provider. The amount of connections required is defined bythe number of users being hosted on the PBX and the capability of thePBX to share these connections amongst multiple users.

Continuing to refer to FIG. 1, Caller 170 represents conference host orconference participants external to the Enterprise 185. For the purposeof this embodiment, Caller 170 represents any caller needing to host orjoin a conference call via the PSTN 175 hosted by the ConferencingService Provider 190. As is illustrated in the diagram, connectivitybetween the PSTN 175 and the entry point into the Conferencing ServiceProvider's network is supplied by Circuit-Switched Connections 130.These connections can be of many varieties and are only limited by theinterface connectivity method supported by the Conferencing ServiceProvider's Media Gateway 135 and the PSTN 175. For the purpose of thisinvention, it should be assumed that this connectivity is DS1/DS3 (NorthAmerican) or E1/E3 (International) based. It should also be assumed thatPSTN 175 does not need to reside in the same geographical region as theConferencing Service Provider. The Enterprise 185 and PSTN 175 couldreside internationally with the Conferencing Service Provider residinglocally.

The Conferencing Service Provider 190 is an entity that providesconferencing services to enterprises or other business entities. For thepurposes of this embodiment, it is made up of multiple components allnetworked together to perform the service. The entities of this platforminclude the Media Gateway 135, Media Servers 140 and 145, an ApplicationServer 155, and a networking backbone 180 that links all componentstogether.

Media Gateway 135 is the device that interfaces directly with the PSTNand supplies the conversion of the circuit-switched conference call toan Internet Protocol (IP) stream and vice versa for processing withinthe conferencing system. The Media Gateway uses the Session InitiatedProtocol (SIP) or similar IP control-plane protocol for sessionestablishment and maintenance with the other components in the system.It uses the Real Time Reservation Protocol (RTP) or similar bearer-planeprotocol for establishing bearer-plane Voice over IP (VoIP) connectionsin the system. Media Servers 140/145 in the Conferencing System 190 areused to host the conference calls and supply all features associate withconferencing. These systems are well known in the art and can be made upof common forms of processing medium capable of running commerciallyavailable software suites providing SIP conferencing or similar IPtelephony based software packages. The Media Servers 140/145 areassigned to specific conferences by the Application Server 155. TheApplication Server 155 is the heart of the conferencing system andprovides all initial call setup processing and resource managementwithin the system. It receives SIP calls from the Media Gateway 135 andestablishes conference sessions via RTP between the Media Gateway 135and Media Servers 140/145. It controls call flow and conference businesslogic within the system.

FIG. 1 represents the current connectivity that exists between theEnterprise System 185 and the Conferencing Service Provider 190.Circuit-switched connectivity 110 can be costly for an Enterprise Systemto maintain and drives the need for alternative methods for multipleconference call traffic to the external Conferencing Service Provider.

With reference now to FIG. 2, a recommended conference call routingmechanism is depicted in accordance with a preferred embodiment of thepresent invention. FIG. 2 shows the addition of a Media Gateway 210, IPBackbone Network 280, Media Server-1 215, Media Server-2 220, and Router225. These devices are added at the Enterprise System 285 premise formaintaining local conference call establishment and Internet Protocolrouting of conference calls over the Wide Area Network 230 to theConferencing Service Provider 290. These devices allow the “bridging” ormixing of conference callers external to the enterprise with conferencecallers within the enterprise.

In the depicted figure and with particular reference to EnterpriseSystem 285, Callers 200 are interfaced to PBX 205 and are eitherconference hosts or conference participants with respect to the currentinvention. PBX 205 hosts these callers and performs telephony routingand call maintenance. Multiple circuit-switched connections leaving PBX205 interface with a Media Gateway 210. The Media Gateway 210 convertsthe circuit switched connections into IP based sessions and communicatesdirectly with the Application Server 255 at the Conferencing ServiceProvider 290 via Routers 225 and 250 and the Wide Area Network (WAN)230. The Application Server 255 is the main interface server in theConferencing Service Provider 290 network. It serves as a proxy serverto all of the other SIP entities in the network and maintains locationbased data of all Media Server entities both internal and external tothe network. It also performs the associated routing necessary toestablish and maintain the conferences. It performs all resourcemanagement within the network and maintains information on availableMedia Server resources and allocates these resources as requested.

With reference now to FIG. 3, a logical connectivity diagram is depictedin accordance with a preferred embodiment of the present invention. Asdiscussed in FIG. 2, Callers 300 communicate with the PBX in a formatthat is supported by that PBX. These Interfaces 373 are beyond the scopeof this invention. For simplification purposes, it will be assumed thatthese Interfaces 373 are circuit-switched TDM interfaces. It is alsoassumed that Interface 373 exists between the PBX 305 and the MediaGateway 310. This interface is driven by the supported media interfacecards supported by the Media Server 310 and is beyond the scope of thisinvention. As Callers 300 either establish or attempt to joinconferences, Media Server 310 communicates with Application Server 355.At this point in the invention, all communication is based on IPTelephony protocols. These protocols can be any IP Telephony protocolsthat support session establishment/management as well as Real-Time Voiceover IP. For the purposes of this invention, it will be assumed that allsession based IP telephony is SIP based and all Voice over IP is RTP.

Continuing to reference FIG. 3 along with referencing FIG. 4 as amessage flow reference, and assuming a conference call is beingattempted to be setup by one of Callers 300, a SIP INVITE 400 messagewould be exchanged between the Media Gateway 310 and the Media Server 1315 for establishing a session to support this call between theseentities. Media Server 1 315 then initiates a CALL WAITING 405 messageto Application Server 355 to establish the Conference Call resources atthe Conferencing Service Provider 390. Application Server 355 verifiesthat caller is authorized to establish a conference on this system. Oncethis is verified, it will respond back to the Media Server 1 315 with anACCEPT CALL response. Media Server 1 315 then responds back to the MediaGateway 310 with a SIP 200 OK 410 message. Media Gateway 410 willacknowledge this with a SIP ACK back to Media Server 1 315. With thesession now established between the Media Gateway 310 and Media Server315, an RTP session 415 is opened between the two devices. While RTPlinkage is established between the Media Gateway and Media Server at thecustomer premise, a PROMPT AND COLLECT 420 is sent from the ApplicationServer 355 to Media Server 1 315 to gather entered data by Caller 300for establishing the conference. Media Server 1 315 returns this data toApplication Server 355 via a DTMF COLLECTED message. After theApplication Server 355 has this data, it sends a SIP INFO (CreateConference) 425 message to Media Server 2 320 at Enterprise site. MediaServer 2 320 responds with a SIP 200 OK message to acknowledge andconfirm receipt. Based on the Application Server 355 selecting MediaServer 2 320 to host the call, the Application Server 355 sends a CALLTRANSFER 430 message to Media Server 1 315 to transfer the call. Itcontains the appropriate routing information to share with the MediaGateway for re-establishment of call on a different Media Server. MediaServer 1 315 initiates a SIP REFER 435 message to the Media Gateway 310.Media Gateway 310 utilizes new information supplied by Media Server 1 toattempt establishment of session with Media Server 2 320 by sending it aSIP INVITE 440 message. Media Server 2 320 invokes a CALL WAITING 445message to Application Server to confirm request by Media Gateway.Application Server 355 confirms that caller is valid and conference isalready established and sends an ACCEPT CALL response back to MediaServer 2 320. At this point, the Media Server 2 can respond to the MediaGateway with a SIP 200 OK message letting it know that the session isestablished. The Media Gateway 310 then responds with a SIP ACK 450 todo the final handshake with Media Server 2 320. At this point, an RTPlink 455 is established between the Media Gateway and Media Server 2.Once this new RTP session is established, the Media Gateway 310 notifiesthe Media Server 1 315 that it can tear down the RTP session that wasestablished between them. This is done via a SIP NOTIFY 460 message sentto the Media Server 1. The Media Server 1 responds back with a SIP 200OK message and cleans up resources allocated for that RTP session. Atthis point in the process, the Enterprise Caller is in a conference onMedia Server 2 at the Enterprise.

Continuing to reference FIG. 3 and now referring to FIG. 5 as messageflow reference, PSTN Caller 370 is attempting to join a conferencehosted at the Enterprise 385. PSTN Caller 370 enters the appropriatenumbers to access the conference call. The PSTN 375, once receiving thisdial string, routes the call to the Media Gateway 335 at theConferencing Service Provider 390. The Media Gateway performs theappropriate circuit to packet translation on the incoming data and sendsa SIP INVITE 500 message to the Media Server 1 340. Media Server 1 340then initiates a CALL WAITING 505 message to Application Server 355 toestablish the callers access privileges at the Conferencing ServiceProvider 390. Application Server 355 verifies that caller is authorizedto establish a conference on this system. Once this is verified, it willrespond back to the Media Server 1 340 with an ACCEPT CALL response.Media Server 1 340 then responds back to the Media Gateway 335 with aSIP 200 OK 510 message. Media Gateway 335 will acknowledge this with aSIP ACK back to Media Server 1 340. With the session now establishedbetween the Media Gateway 335 and Media Server 340, an RTP session 515is opened between the two devices. While RTP linkage is establishedbetween the Media Gateway and Media Server at the Conferencing ServiceProvider premise, a PROMPT AND COLLECT 520 is sent from the ApplicationServer 355 to Media Server 1 340 to gather entered data by Caller 370for establishing the conference. Media Server 1 340 returns this data toApplication Server 355 via a DTMF COLLECTED message. Application Server355 scans its current, established conferences via its internal databaseand knows that this caller wants to access a conference that alreadyexists on the Enterprise 385 system. After the Application Server 355determines this, it sends a SIP INFO (Create Conference) 525 message toMedia Server 2 345 to allocate conference resources to this user. MediaServer 2 345 responds with a SIP 200 OK message to acknowledge andconfirm receipt. At this point in the session, the Application Server355 sends a SIP INFO (Bridge Mixers) 530 message to Media Server 2 345and a SIP INFO (Bridge Mixers) 535 to Media Server 2 320 at Enterprisesite. At this point, Application Server 355 creates a conference at theMedia Sever located at the Conferencing Service Provider Site andbridges it with the conference on the Media Server at the Enterpriselocation. Once each Media Server receives the action to bridge themixers, an RTP Session 540 is established between these entities. Basedon the Application Server 355 selecting Media Server 2 345 to host thecall, the Application Server 355 sends a CALL TRANSFER 545 message toMedia Server 1 340 to transfer the call. It contains the appropriaterouting information to share with the Media Gateway for re-establishmentof call on a different Media Server. Media Server 1 340 then initiates aSIP REFER 550 message to the Media Gateway 335. Media Gateway 335utilizes new information supplied by Media Server 1 to attemptestablishment of session with Media Server 2 345 by sending it a SIPINVITE 555 message. Media Server 2 345 invokes a CALL WAITING 560message to Application Server to confirm request by Media Gateway.Application Server 355 confirms that caller is valid and conference isalready established and sends an ACCEPT CALL response back to MediaServer 2 345. At this point, the Media Server 2 can respond to the MediaGateway with a SIP 200 OK message letting it know that the session isestablished. The Media Gateway 335 then responds with a SIP ACK 565 todo the final handshake with Media Server 2 345. At this point, an RTPlink 570 is established between the Media Gateway and Media Server 2.Once this new RTP session is established, the Media Gateway 335 notifiesthe Media Server 1 340 that it can tear down the RTP session that wasestablished between them. This is done via a SIP NOTIFY 575 message sentto the Media Server 1. The Media Server 1 responds back with a SIP 200OK message and cleans up resources allocated for that RTP session. Atthis point in the process, the PSTN Caller is in a conference on MediaServer 2 at the Conferencing Service Provider site bridged with theEnterprise Caller on the Media Server 2 conference at the Enterpriselocation.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Forexample, although the processes and apparatus of present invention areillustrated with voice conferencing and SIP/RTP IP Telephony messaging,the processes and apparatus of the present invention may be implementedin other types of networks and protocols. For example, the presentinvention may be illustrated in SIP/RTP protocols or MPLS (MultiProtocol Label Switching)/RSVP (Resource Reservation Protocol). Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method, comprising: exchanging a first SIPINVITE message between a Media Gateway of an Enterprise and a firstMedia Server of the Enterprise; initiating a CALL WAITING message fromthe first Media Server to an Application Server of a ConferencingService Provider to establish conference call resources at theConferencing Service Provider; verifying at the Application Server thata caller initiating the first SIP INVITE message is authorized toestablish the Enterprise conferencing; sending a PROMPT AND COLLECTmessage from the Application Server to the first Media Server; andacknowledging a response from the first Media Server by the MediaGateway.
 2. The method of claim 1, further comprising: opening a firstRTP session between the Media Gateway and the first Media Server; andcollecting and sending data from the caller to establish the Enterpriseconferencing and from the first Media Server to the Application Servervia a DTMF COLLECTED message.
 3. The method of claim 2, furthercomprising: after receipt of the data by the Application Server, sendinga SIP INFO message from the Application Server to a second Media Serverof the Enterprise; acknowledging receipt of the SIP INFO message at thesecond Media Server and selection by the Application Server of thesecond Media Server to host a call; and sending a CALL TRANSFER messagefrom the Application Server to the first Media Server to transfer thecall.
 4. The method of claim 3, wherein the CALL TRANSFER messageincludes routing information operable to be shared with the MediaGateway for establishment of the call on the second Media Server.
 5. Themethod of claim 3, further comprising: sending a SIP REFER message fromthe first Media Server to the Media Gateway, wherein the SIP REFERmessage includes information about the second Media Server; and usingthe information about the second Media Server from the SIP REFERmessage, and exchanging a second SIP INVITE message between the MediaGateway and the second Media Server.
 6. The method of claim 5, furthercomprising: sending a CALL WAITING message from the second Media Serverto the Application Server to confirm the second SIP INVITE message fromthe Media Gateway; sending an ACCEPT CALL response from the ApplicationServer to the second Media Server indicating that a conference call hasbeen established; establishing a second RTP session between the MediaGateway and the second Media Server; and terminating the first RTPsession between the Media Gateway and the first Media Server.
 7. Amethod, comprising: connecting a communication device with a MediaGateway at a Conferencing Service Provider through a PSTN; sending afirst SIP INVITE message from the Media Gateway to a first Media Serverat the Conferencing Service Provider; sending a CALL WAITING messagefrom the first Media Server to an Application Server at the ConferencingService Provider; verifying at the Application Server that a caller hasaccess privileges for an established conference call; upon verification,sending an ACCEPT CALL message from the Application Server to the firstMedia Server; sending a PROMPT AND COLLECT message from the ApplicationServer to the first Media Server; and sending an acknowledgement messagefrom the Media Gateway to the first Media Server.
 8. The method forjoining a conference call hosted at an Enterprise of claim 7, furthercomprising: opening a first RTP session between the Media Gateway andthe first Media Server; and collecting and sending data from a callrequesting to join the established conference call and from the firstMedia Server to the Application Server via a DTMF COLLECTED message. 9.The method of claim 8, further comprising: after receipt of the data bythe Application Server, scanning a database of the Application Server todetermine that the established conference call still exists; upondetermination, sending a CREATE CONFERENCE message from the ApplicationServer to a second Media Server at the Conferencing Service Provider toallocate resources to the caller; responding to the CREATE CONFERENCEmessage to acknowledge receipt of the CREATE CONFERENCE message at thesecond Media Server; and sending a first BRIDGE MIXERS message from theApplication Server to the second Media Server at the ConferencingService Provider and sending a second BRIDGE MIXERS message from theApplication Server to a third Media Server at the Enterprise site. 10.The method of claim 9, further comprising bridging Mixers to establish asecond RTP Session between the third Media Server and the second MediaServer.
 11. The method of claim 10, further comprising sending a CALLTRANSFER message from the Application Server to the first Media Serverto transfer the call.
 12. The method of claim 11, wherein the CALLTRANSFER message includes routing information operable to be shared withthe Media Gateway for establishment of the call on the second MediaServer.
 13. The method of claim 12, further comprising: sending a SIPREFER message from the first Media Server to the Media Gateway, whereinthe SIP REFER message includes information about the second MediaServer; and using the information about the second Media Server from theSIP REFER message, and exchanging a second SIP INVITE message betweenthe Media Gateway and the second Media Server.
 14. The method of claim13, further comprising: sending a CALL WAITING message from the secondMedia Server to the Application Server to confirm the second SIP INVITEmessage from the Media Gateway; sending an ACCEPT CALL response from theApplication Server to the second Media Server; establishing a second RTPsession between the Media Gateway and the second Media Server; andterminating the first RTP session between the Media Gateway and thefirst Media Server.
 15. A non-transitory computer readable mediumcomprising instructions that when executed by a processor perform:exchanging a first SIP INVITE message between a Media Gateway of theEnterprise and a first Media Server of the Enterprise; initiating a CALLWAITING message from the first Media Server to an Application Server ofa Conferencing Service Provider to establish conference call resourcesat the Conferencing Service Provider; verifying at the ApplicationServer that a caller initiating the first SIP INVITE message isauthorized to establish the Enterprise conferencing, and uponverification; sending a PROMPT AND COLLECT message from the ApplicationServer to the first Media Server; and receiving acknowledgement of theresponse from the first Media Server with a SIP ACK message from theMedia Gateway.
 16. The non-transitory computer readable medium of claim15, comprising instructions that when executed by the processor performreceiving gathered data from the call requesting to join the establishedconference call and from the first Media Server at the ApplicationServer in a form of a DTMF COLLECTED message.
 17. The non-transitorycomputer readable medium of claim 16, comprising instructions that whenexecuted by the processor perform: after receipt of the data by theApplication Server, sending a SIP INFO message from the ApplicationServer to a second Media Server of the Enterprise; acknowledging receiptof the SIP INFO message at the second Media Server and selection by theApplication Server of the second Media Server to host a call; andsending a CALL TRANSFER message from the Application Server to the firstMedia Server to transfer the call.
 18. The non-transitory computerreadable medium of claim 17, wherein the CALL TRANSFER message includesrouting information operable to be shared with the Media Gateway forestablishment of the call on the second Media Server.
 19. Thenon-transitory computer readable medium of claim 17, comprisinginstructions that when executed by the processor perform: sending a SIPREFER message from the first Media Server to the Media Gateway, whereinthe SIP REFER message includes information about the second MediaServer; and using the information about the second Media Server from theSIP REFER message, exchanging a second SIP INVITE message between theMedia Gateway and the second Media Server.
 20. The non-transitorycomputer readable medium of claim of claim 19, comprising instructionsthat when executed by the processor perform: sending a CALL WAITINGmessage from the second Media Server to the Application Server toconfirm the second SIP INVITE message from the Media Gateway; sending anACCEPT CALL response from the Application Server to the second MediaServer indicating that a conference call has been established;establishing a second RTP session between the Media Gateway and thesecond Media Server; and terminating the first RTP session between theMedia Gateway and the first Media Server.